1. Technical Field
This disclosure relates to a development roller used for copying machines, facsimiles, printers or the like, more specifically to a development roller which includes a development sleeve disposed adjacently to a photo-conductive drum and a magnetic roller disposed in the development sleeve and in which a developer including a toner and a magnetic carrier is adsorbed to an outer surface of the development sleeve by a magnetic force of the magnet roller, a surface treatment device configured to treat the outer surface of the development sleeve, and a wire member used to roughen the outer surface of the development sleeve.
2. Description of Related Art
According to the prior art, in order for the developing sleeve of the development roller of the development device to carry the developer and surely convey the developer to the photo-conductive drum, the sand blast processing and so on are executed on an external surface of the developing sleeve described above (For example, see the Patent Documents 1 to 3 described below), or the grooves are formed on the external surface of the developing sleeve, or the linear material is randomly collide with the external surface by the rotating magnetic field, what is called, the electromagnetic blast processing has been executed on the external surface of the developing sleeve.
By performing the sand blast processing described above or forming the depressions, the developer slips and is stagnant on the external surface of the developing sleeve which rotates at high speed, and the developer also prevents the deterioration in the density of the images.
Although the developing sleeve on which the above-described sand blast processing is performed is composed of any of aluminum alloy, brass, stainless steel, and electrically conductive resin, it often is comprised of aluminum alloy in order to reduce the cost and enhance the processing precision. In the case where the external surface of the developing sleeve comprised of aluminum alloy is subjected to the sand blast processing, for example, an aluminum tube which is extruded into a developing sleeve-like extrusion at high temperature is subjected to the cold blowing of grindstone powder, thereby making the surface uneven.
The surface roughness is formed to a degree of Rz 5.0 to 15 μm. In the developing sleeve of which the external surface is subjected to the sand blast processing, if the developing sleeve rotates at high speed, the developer engages the uneven surface and thus the slippage is prevented from occurring. However, since the uneven portions formed on the external surface are very fine, the unevenness is gradually scraped away by the developer and so on. For this reason, the uneven portions of the developing sleeve subjected to the sand blast processing are scraped away to be flattened as the number of printed sheets increases or with the change over time. Thus, the developing sleeve subjected to the sand blast processing has a problem in that the conveying amount of the developer is gradually decreased and the thus formed images gradually become light-colored. As such, the developing sleeve subjected to the sand blast processing has a problem of endurance. Although it is possible for the developing sleeve to be made of stainless steel having a high hardness or to be subjected to the sand blast processing, they lead to cost increase and are thus not desirable.
Further, although the developing sleeve on which the above-described sand blast processing is performed is composed of any of aluminum alloy, brass, stainless steel, and electrically conductive resin, it is often comprised of aluminum alloy in order to reduce the cost and enhance the processing precision similar to the above. In the case where the external surface of the developing sleeve comprised of aluminum alloy is subjected to forming the depressions, for example, an aluminum tube which is extruded into a developing sleeve-like extrusion at high temperature is subjected to the cold extruding, thereby forming the depressions thereon by the dice. As the cross-sectional shape of each groove, a rectangular shape, V-shape, U-shape and so on are general. Further, the depth of each of the depressions in the order of 0.2 mm and the number of grooves in the order of 50 for the developing sleeve having an external diameter of φ25 mm are general.
In the developing sleeve of which the external surface is subjected to forming the depressions, if the developing sleeve rotates at high speed, the developer engages in the grooves and thus the slippage is prevented from occurring. Further, since the developing sleeve of which the external surface is formed with the depressions is considerably larger than the developing sleeve on which the sand blast processing is performed, the grooves are not likely to be worn away and the conveying amount of developer is never deteriorated. Namely, the developing sleeve of which the external surface is formed with the depressions is less worn away for use in the long-term as compared with the developing sleeve on which the sand blast processing is performed, thereby enabling the safe convey of the developer.
However, in the developing sleeve of which the external surface is formed with the depressions, since the amount of developer conveyed through the grooves is larger than the amount of developer conveyed through the portions being not formed with the depressions, the periodical variation in the image density due to the formation of the grooves or the variation in pitch tends to occur. Generally, although the deeper the grooves become, the larger the conveying amount of the developer, the variation in pitch by the differences of the developing electrical field strength and so on due to the formation of the grooves or not tends to occur. On the one hand, if the grooves are shallow, the variation in pitch does not tend to occur from the viewpoint of the developing electrical field strength. However, if the toner or an additive, or the carrier in the developer is/are filled, the deterioration degree of the conveying performance of the developer becomes large, the variation in pitch tends to occur due to the lack of the absorbing amount of the developer.
Now, as the solution to the above-described problems, JP2003-255692A (Patent Document 1) describes that the depth of each of the grooves is defined as not less than 0.05 mm and not more than 0.15 mm so as to prevent the variation in pitch from occurring and try to maintain the conveying performance of the developer. However, in recent years, in order to obtain a high quality image, since the image reproducibility is enhanced due to the progress of the image forming technology by the adoption of smaller particle diameter toner or smaller particle diameter carrier, the variation in pitch tends to conspicuously occur. For this reason, even if the image forming device disclosed in JP2003-255692A is adopted, there tends to occur the variation in pitch.
The reason for this will be reviewed. As shown in FIGS. 33 and 34, in the development region D where the developing sleeve 200 and the photo-conductive drum 201 face each other, on the external surface of the developing sleeve 200 on which grooves 202 are not formed, the developer 203 slips and thus the amount of developer 203 is reduced. This was due to the deterioration in density (density). In general, although the developer 203 moves in the development region D where the developing sleeve 200 and the photo-conductive drum 201 face each other, it is necessary to convey a large quantity of developer 203 so as to obtain the sufficient image density.
For this reason, usually, the development sleeve 200 is driven to rotate by the surface speed which is 1.1 to 2.5 times larger than that of the photo-conductive drum 201. When the developer 203 rotates at high speed and passes through the development region D, the friction of the developer 203 with the photo-conductive drum 201 which rotates at relatively low speed becomes a load resistance. On the external surface of the developing sleeve 132 where grooves are not formed, as shown in FIG. 33, the slippage of the developer 203 or the lack of the absorbing amount of the developer tends to occur. For this reason, in the development region D, the amount of developer in the downstream side compared with that in the upstream side along the rotating direction of the developing sleeve 200 is reduced. On the one side, as shown in FIG. 34, since the sufficient conveying force can be obtained while the depressions pass through the development region D, the slippage does not occur and the absorbing amount of the developer is sufficient. Namely, in a period of the grooves 202 which pass through the development region D, the amount of the developer 203 varies depending upon whether the slippage occurs or not and the variation in pitch due to the difference of image density occurs.
JP2004-191835A (Patent Document 2) proposes an image forming device in which the toner of which a volumetric average particle diameter of not less than 4 μm and not more than 8.5 μm is used as the developer on the external surface of the developing sleeve is formed with a plurality of grooves which extend along the longitudinal direction of the developing sleeve, and the interval between the depressions which are adjacent with each other is adapted to be smaller than the traveling direction width of the photo-conductive drum in the development region where the developer contacts the photo-conductive drum. According to this image forming device, there always exists at least one groove of the developing sleeve, the groove suppressing the slippage of the developer which is carried on the developing sleeve. Thus, it is possible to suppress the variation in the amount of the developer in the development region as compared with the case where no grooves of the developing sleeve exist in the development region. Whereby, even if the toner having volumetric average particle diameter of not less than 8.5 μm is used, it is possible to form a high quality image having good image reproducibility and not to make the variation in pitch due to the difference of image density stand out.
According to the developing sleeve disclosed in JP2004-191835A described above, it is necessary to make the interval between the grooves narrower. The method in which an aluminum tube is subjected to the cold extruding and then forming the grooves thereon by the dice has reached the limit. Even if further grooves are processed in the interval between the grooves in which additional grooves are possible to be formed, since the deviation in the depth of each of the grooves increases in the cutting process or the grinding process as external diameter finishing, the variation in image density of the deviation in the depth of each of the grooves occurs.
On the one hand, in the processing method in which one groove or a plurality of grooves is/are simultaneously formed or cut as a method of forming depressions, although it is possible to make the interval between the grooves narrower or to reduce the deviation of the depth of each of the grooves, nevertheless, the number of processes is increased and thus such an increase leads to cost increase of the product.
Further, JP2007-86091 (Patent Document 3) discloses an electromagnetic blast processing by which it is possible to suppress the deterioration in the conveying amount of the developer due to the change over time, but since the linear material randomly collides with the external surface of the developing sleeve, it is difficult to set up the process condition capable of achieving the long life span while ensuring the optimal absorbing amount of the developer, and thus there arises a problem in that it is difficult to handle with the further increase of the absorbing amount of the developer in order to maintain the high quality in the future high speed machine.
In order to balance the suppression of a lowering of the conveying amount of the developer due to this kind of change over time and the prevention of the occurrence of the variation in pitch, the applicant of the present application proposes that the tip end of the end mill as the rotating tool which rotates around the axis of rotation thereof is abut against the external surface of the developing sleeve, the end mill and the developing sleeve are relatively moved along the longitudinal direction of the developing sleeve while rotating the developing sleeve around the axis of rotation of the developing sleeve, and the depressions are formed on the external surface of the developing sleeve so that both ends of the depressions which are adjacent with each other on the external surface of the developing sleeve are spaced with each other.
In the developing sleeve formed as described above, since such projections which are formed by the conventional sand blast processing are not formed and each of the depressions are formed larger than the projections which are formed by the conventional sand blast processing, the depressions are likely to be worn away by the change over time. Thus, it is possible to suppress the lowering of the conveying amount of the developer. Further, since a large number of the depressions are arranged in a spaced manner so that the depressions formed on the external surface are not overlapped with each other, the developer is collected in the depressions, so that the portions in which the developer is collected are formed on the external surface in a uniformly spaced manner. Accordingly, it is possible to prevent the variation in image from occurring.
However, in the developing sleeve on which external surface is formed with depressions by the end mill, if the roundness and the coaxiality of the sleeve prior to processing are low, the distance between the end mill and the external surface of the developing sleeve varies when processing the depressions. As such, if the distance between the end mill and the external surface of the developing sleeve varies, the planar shape of each of the depressions becomes larger or smaller. Thus, since large depressions and small depressions are unevenly distributed along the circumferential direction of the developing sleeve, the variation in conveying force of the developer occurs along the circumferential direction of the developing sleeve. Accordingly, one portions wherein the absorbing amount of the developer is large and the other portions wherein the absorbing amount of the developer is small when the developing sleeve rotates, are alternately occurred. Since the image density is dark in the portion where the absorbing amount of the developer is large and the image density is light in the portion where the absorbing amount of the developer is small, the variation in image density occurs.
It is necessary to make the deviation in depth of each of the depressions not more than 10 μm in order to prevent the variation in image density from occurring. For this reason, the developing sleeve prior to performing the surface treatment needs to have the roundness or the coaxiality of the high precision order such as not more than 10 μm, thus the developing sleeve is not available and this is not practical.